The present invention relates to a communication apparatus and a communication method of a multi carrier transmission system, and in particular, to a communication apparatus and a communication method using a multi carrier transmission method (Digital Wavelet Multi Carrier transmission system, hereinafter, described as “DWMC transmission system”) which carries out data transmission by digital modulating and demodulating processing with the use of a real coefficient wavelet filter bank.
In a terrestrial digital broadcasting system etc., wide band data transmission is enabled by a multi carrier transmission system with the use of OFDM (Orthogonal Frequency Division Multiplexing). As a data transmission system depending on this type of the multi carrier transmission system with the use of OFDM, a multi carrier transmission method depending on digital modem processing with the use of a real coefficient wavelet filter bank (DWMC transmission method) has been proposed. In the DWMC transmission method, a plurality of digital modulated waves are combined by use of the real coefficient filter bank, and thereby, transmission signals are generated. As a modulation system of each carrier, PAM (Pulse Amplitude Modulation) etc. are used.
Data transmission, which depends on the DWMC transmission method, will be described by use of FIGS. 15 to 18. FIG. 15 is a view which shows an example of an wavelet wave form, and FIG. 16 is a view which shows an example of a transmission wave form in the DWMC transmission method, and FIG. 17 is a view which shows an example of a transmission spectrum in the DWMC transmission method, and FIG. 18 is a view which shows a configuration example of a transmission frame in the DWMC transmission method.
In the data transmission which depends on the DWMC transmission method, as shown in FIG. 15, impulse responses of each sub carrier are transmitted over being overlapped in each sub carrier. Each transmission symbol becomes such a time wave form that impulse responses of each sub carrier were combined, as shown in FIG. 16. An example of an amplitude spectrum is shown in FIG. 17. In the DWMC transmission method, approximately several dozen through several hundred of transmission symbols in FIG. 16 are collected to configure one transmission frame. A configuration frame of the DWMC transmission frame is shown in FIG. 18. In this DWMC transmission frame, a symbol for frame synchronization, a symbol for equalization etc. are included in addition to a symbol for information data transmission.
FIG. 19 is a block diagram which shows a conceptual configuration of a communication apparatus as a past example, which is configured by having a transmitting device and a receiving device in case that the DWMC transmission system was adopted.
In FIG. 19, a receiving device 199 is configured by having an A/D converter 110 which carries out analog-digital conversion, a wavelet transform unit 120 which carries out discrete wavelet transformation, a parallel/serial (P/S) converter 130 which converts parallel data into serial data, and a decision unit 140 which carries out judgment of received signals. A transmitting device 299 is configured by having a symbol mapper 210 which converts bit data into symbol data to carry out symbol mapping, a serial/parallel (S/P) converter 220 which converts serial data into parallel data, an inverse wavelet transform unit 230 which carries out inverse discrete wavelet transformation, and a D/A converter 240 which carries out digital-analog conversion.
An operation of the communication apparatus with the above-described configuration will be described. Firstly, in the transmitting device 299, bit data of transmission data is converted into symbol data by the symbol mapper 210, and symbol mapping (PAM) is carried out in accordance with each symbol data. Then, serial data is converted into parallel data by the S/P converter 220, and thereby, a real number value di (i=1˜M, M is a plural number) is given to symbol data with respect to each sub carrier. After that, this real number value is inverse discrete wavelet transformed on a time axis by the inverse wavelet transform unit 230. By this means, sample values of time axis wave forms are generated, and a sample value series, which represents transmission symbols, is generated. Then, this sample value series is converted into analog base band signal wave forms which are continuing in terms of time by the D/A converter 240, and then, transmitted. Here, the number of sample values on a times axis, which are generated by the inverse discrete wavelet transformation, is normally 2 to the n-th power pieces (n is a positive integer).
In the receiving device 199, analog base band signal wave forms, which are obtained from received signals, are sampled with the same sample rate as that of a transmitting side by the A/D converter 110, to obtain a sample value series. Then, this sample value series is discrete wavelet transformed on a frequency axis by the wavelet transform unit 120, and parallel data is converted into serial data by the P/S converter 130. Finally, an amplitude value of each sub carrier is calculated in the decision unit 140, and judgment of a received signal is carried out to obtain reception data.
In addition, as an example of the communication apparatus with the use of the DWMC transmission method, proposed is a power line carrier communication apparatus which carries out data transmission by utilizing a power line which were disposed in a house etc., as communication medium (e.g., see, JP-A-2003-218831).
In the meantime, in the multi carrier transmission system, there is a case to dispose a pilot symbol for transmitting a pilot signal by use of a sine wave signal in a predetermined symbol, in order to carry out adjustment etc. of a phase of transmission data. By information of this pilot symbol, it becomes possible to adjust an amplitude and a phase of transmission data, and to improve an equalization characteristic of a channel characteristic (compensation of a transmission characteristic, etc.) between a transmitting device and a receiving device.
A past multi carrier transmission system with the use of FFT (Fast Fourier Transform) based OFDM is one which carries out FFT as complex number conversion, and therefore, it is possible to generate a pilot symbol having complex information which represents an amplitude and a phase, only by transmitting a known signal (e.g., a signal in which identical data such as all 1 continues) by use of one symbol, in case of disposing a pilot symbol (e.g., see, JP-A-2000-278237).
In contrast to this, a multi carrier transmission system, which depends on wavelet transformation based OFDM to be used in the DWMC transmission method, is one which carried out wavelet transformation as real number conversion, and in addition, even if a pilot symbol, which was simply configured by one symbol, is demodulated, it is not possible to obtain complex information since a filter length is longer than a symbol length, and therefore, in the multi carrier transmission system which depends on wavelet transformation based OFDM, a pilot symbol was not used.